It takes a while, but this is currently the Only way to remove accounts that I know of. First export the private keys of the accounts you want to use using the following command in console:
wallet_dump_private_key <account name>
Copy the private key for any account with a balance and note the account name they are associated with. Remember to store these keys in a safe place.. Like Bitcoin private keys, if anyone gets them they can steal your wallet without your password.
Quit the BTSX client.
Delete this folder: C:\Users\UserName\AppData\Roaming\BitShares X\wallets\default
^ Note: replace UserName with your Windows user name; AppData is a hidden folder so you need to type it in manually or turn on the viewing of hidden files and folders ^
Re-Open the BitsharesX client, create a new wallet password, and wait for the block chain to finish downloading. Instead of creating a new account, just go to console to do the following.
Import your private key to your account(s) using the 'wallet_import_private_key' command in the console with the private keys you copied earlier using the following syntax (only import the private keys to the accounts you want, and not the unregistered accounts!!)
wallet_import_private_key <private key>
Rescan the block chain to retrieve all of your transactions and to show your proper balance using the following command in console: